commit 3574c37f98abec8bd2e1ba37c65997aa63d0eb0b
author Tom Cherry <tomcherry@google.com> Fri Feb 21 15:06:46 2020 -0800
committer Tom Cherry <tomcherry@google.com> Fri Feb 21 16:37:43 2020 -0800
tree 532db587151127313385ccb6b05aab24144d7f71
parent e53f8b8f9d0c52e927f970b42146f203611798d2

liblog: add __attribute__((uninitialized)) to liblog buffers

These buffers are immediately written into with *printf() and are in
the hot path, so do not initialize them.  This saves ~70ns off of each
log message, which is ~14% of the overhead within
__android_log_print() when writing to a no-op logger.

Test: liblog benchmarks
Change-Id: I2b898e72c75b57bc63fee565b49a4e00e377ed1a

liblog/logger_write.cpp

diff --git a/liblog/logger_write.cpp b/liblog/logger_write.cpp
index cf82e0f..1b6b0c6 100644
--- a/liblog/logger_write.cpp
+++ b/liblog/logger_write.cpp
@@ -348,7 +348,7 @@
     return 0;
   }
 
-  char buf[LOG_BUF_SIZE];
+  __attribute__((uninitialized)) char buf[LOG_BUF_SIZE];
 
   vsnprintf(buf, LOG_BUF_SIZE, fmt, ap);
 
@@ -366,7 +366,7 @@
   }
 
   va_list ap;
-  char buf[LOG_BUF_SIZE];
+  __attribute__((uninitialized)) char buf[LOG_BUF_SIZE];
 
   va_start(ap, fmt);
   vsnprintf(buf, LOG_BUF_SIZE, fmt, ap);
@@ -386,7 +386,7 @@
   }
 
   va_list ap;
-  char buf[LOG_BUF_SIZE];
+  __attribute__((uninitialized)) char buf[LOG_BUF_SIZE];
 
   va_start(ap, fmt);
   vsnprintf(buf, LOG_BUF_SIZE, fmt, ap);
@@ -398,7 +398,7 @@
 }
 
 void __android_log_assert(const char* cond, const char* tag, const char* fmt, ...) {
-  char buf[LOG_BUF_SIZE];
+  __attribute__((uninitialized)) char buf[LOG_BUF_SIZE];
 
   if (fmt) {
     va_list ap;